It is generally known to apply pneumatic direct fuel injection systems to internal combustion engines. In such systems, fuel is metered for a controlled period of time into the body of an injector a short period of time before the injector opens. High pressure air is provided to the injector such that when the injector opens, the fuel is atomized and blasted into an engine combustion chamber for a controlled period of time after which the injector closes.
In such systems, fuel hangup may occur, wherein a portion of the quantity of fuel metered into the injector remains in the injector after the injector closes. This portion of fuel augments the quantity of fuel available in the injector at the start of the next injection event into the combustion chamber. A deviation away from a desired fueling rate may result from fuel hangup, driving the actual air/fuel ratio blasted into the combustion chamber away from a desired air/fuel ratio, which may degrade engine performance and may increase levels of pollutants emitted by the engine.
During extended periods of steady state engine operation in which the desired fueling rate will not change significantly, fuel hangup may not significantly contribute to deviations away from a desired fueling rate, as the amount of fuel hangup does not substantially vary from injection to injection, and thus a substantially constant quantity of fuel is passed to the combustion chamber during each air injection event. However, during transient maneuvers in which the desired fueling rate changes rapidly, fuel hangup may cause a significant deviation from the desired fueling rate throughout the maneuver.
Accordingly, what is needed is fueling rate compensation for the effects of fuel hangup in pneumatic direct fuel injection systems, especially during transient maneuvers.